rfc:foreach_unwrap_ref

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rfc:foreach_unwrap_ref [2021/08/13 12:45] – created nikicrfc:foreach_unwrap_ref [2021/11/14 17:10] (current) – nikic
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   * Date: 2021-08-13   * Date: 2021-08-13
   * Author: Nikita Popov <nikic@php.net>   * Author: Nikita Popov <nikic@php.net>
-  * Status: Draft+  * Status: Withdrawn
   * Target Version: PHP 8.2   * Target Version: PHP 8.2
   * Implementation: https://github.com/php/php-src/pull/7364   * Implementation: https://github.com/php/php-src/pull/7364
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 ===== Proposal ===== ===== Proposal =====
  
-This RFC proposes to change the semantics of foreach by reference to unwrap the reference after the loop. This means that ''$value'' will still have the value of the last (visited) element, but will no longer be a reference to it.+This RFC proposes to change the semantics of foreach by reference to unwrap the reference after the loop. This means that ''$value'' will still have the value of the last (visited) element, but will no longer be a reference to it. This also applies if the loop is left using ''break'', ''continue'' or ''goto''.
  
 While PHP does not have a dedicated language construct for reference unwrapping, the operation is logically equivalent to: While PHP does not have a dedicated language construct for reference unwrapping, the operation is logically equivalent to:
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 </PHP> </PHP>
  
-Unwrapping the reference requires that we evaluate the variable again after the loop. For a simple variable like ''$value'' this will not have further side effects. For the complex variables in the above example, side effects are possible.+This RFC proposes to only perform the reference unwrapping for simple variables of the form ''$value'' ("CV"), but not for complex variables.
  
-There are broadly two ways we can handle this: Either we always perform the unwrap and accept the potential side effect, or we limit the unwrap operation to only some cases. For all practical purposes, only unwrapping for simple variables would be sufficient.+The reason is that complex variables may have side effects. The most obvious case is ''&$arrayCopy[]'', which would result in an additional null element being appended to ''$arrayCopy'' while attempting the unwrap. The ''&getInfo()['value']'' case could similarly have arbitrary side-effects in the ''getInfo()'' call. Even ''&$info['value']'' might be invoking ''__get()''. 
 + 
 +Use of complex variables as foreach targets is very unusual, so it is rather unlikely that someone will encounter issues with the reused loop variables in this context. Always performing the unwrap would certainly be possible, but the cure seems worse than disease in this instance. 
 + 
 +When foreach is used in conjunction with destructuring, unwrapping will be performed on simple destructuring targets: 
 + 
 +<PHP> 
 +foreach ($array as [&$var, &$complex->var]) {} 
 +</PHP> 
 + 
 +In this example, ''$var'' will be unwrapped because it is a simple variable, while ''$complex->var'' is not affected. As with the non-destructuring case, use of complex variables in this context is unusual and may have side-effects.
  
 ===== Backward Incompatible Changes ===== ===== Backward Incompatible Changes =====
rfc/foreach_unwrap_ref.1628858748.txt.gz · Last modified: 2021/08/13 12:45 by nikic

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